Published on May 8, 2014
Manuel A. Vásquez S. 9-A Biology L2 Earth Layers Presentation 1/4
Crust: • t is the outermost solid shell of a rocky planet or natural satellite, which is chemically distinct from the underlying mantle. The crusts of Earth, the Moon, Mercury, Venus, Mars, Io, and other planetary bodies have been generated largely by igneous processes, and these crusts are richer in incompatible elements than their respective mantles.
Crust and mantle: • The crust of the Earth is composed of a great variety of igneous, metamorphic, and sedimentary ro cks. The crust is underlain by the mantle. The upper part of the mantle is composed mostly of peridotite, a rock denser than rocks common in the overlying crust. The boundary between the crust and mantle is conventionally placed at the Mohorovičić discontinuity, a boundary defined by a contrast in seismic velocity.
Composition: • The continental crust has an average composition similar to that of andesite. Continental crust is enriched in incompatible elements compared to the basaltic ocean crust and much enriched compared to the underlying mantle.
Mantle: • The mantle is a part of a terrestrial planet or other rocky body large enough to have differentiation by density. The interior of Earth, similar to the other terrestrial planets, is chemically divided into layers. The mantle is a layer between the crust and the outer core. Earth's mantle is a silicate rocky shell about 2,900 kilometers (1,800 mi) thick that constitutes about 84% of Earth's volume.
Structure: • The mantle is divided into sections which are based upon results from seismology. These layers (and their thicknesses/depths) are the following: the upper mantle (starting at the Moho, or base of the crust around 7 to 35 km (4.3 to 21.7 mi) downward to 410 km (250 mi)), the transition zone (410–660 km or 250–410 mi), the lower mantle (660–2,891 km or 410–1,796 mi), and anomalous core–mantle boundary with a variable thickness (on average ~200 km (120 mi) thick).
Characteristics: • The mantle differs substantially from the crust in its mechanical properties which is the direct consequence of chemical composition change (expressed as different mineralogy). The distinction between crust and mantle is based on chemistry, rock types, rheology and seismic characteristics. The crust is a solidification product of mantle derived melts, expressed as various degrees of partial melting products during geologic time.
Temperature: • In the mantle, temperatures range between 500 to 900 °C (932 to 1,652 °F) at the upper boundary with the crust; to over 4,000 °C (7,230 °F) at the boundary with the core. Although the higher temperatures far exceed the melting points of the mantle rocks at the surface (about 1200 °C for representative peridotite), the mantle is almost exclusively solid.
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